The present invention relates to rotary drum dryers and especially to rotary drum dryers connected to burners which are used to dry bulk loose materials such as aggregates, and the like.
In the past, it has been common to dry a wide variety of loose materials in large rotating drums. In a typical dryer, a burner which might work on a gas, oil or finely powdered coal might have a blower directing air through the burner for mixing with fuel metered by valves and/or nozzles. The flame is directed in a refractory lined combustion chamber which is open to the drum dryer so that the material being rotated and dispersed in the dryer drum does not interfere with the burner flame and so that the material does not become coated with oil or black carbon by falling through the flame before combustion is complete. The refractory lined combustion chambers, however, are expensive and it is difficult to replace the linings, and in prior systems the flights were attached to the inside of the drum for lifting the material from the bottom as the drum rotated and letting it fall through the air as the heated air passed through the drum to effect a more rapid drying of the material. Flights were designed to distribute the material throughout the interior space of the drum and in a pattern to make the drying as effective as possible. The present invention, on the other hand, is directed towards a flight that distributes the loose material in a drying drum in a pre-determined pattern covering all of the drum except the middle portion where the flame is being directed into the drum. This allows for the elimination of the refractory lined combustion chamber which can accept the high heat of the burner and at the same time prevent the falling material from interfering with the flame and thereby preventing full combustion of the fuel. The loose material also does not become coated with oil or carbon black from falling through that portion of the flame in which there has not been complete combustion of the fuel.